可以使用相关子查询：

select b.*,
       (select a.score
        from a
        where a.name = b.name and a.month <= b.month
        order by a.month desc
        limit 1
       ) as score
from b;

或者，可以使用窗口函数和 join :

select b.*, a.score
from b left join
     (select a.*,
             lead(month) over (partition by name order by month) as next_month
      from a
     ) a
     on b.name = a.name and
        b.month >= a.month and
        (b.month < a.next_month or a.next_month is null);

如果要从中获取多个列，则此方法很方便 a .